Occlumency

Occlumency is the act of magically closing one's mind against Legilimency. It can prevent a Legilimens from accessing one's thoughts and feelings, or influencing them. A person who practises this art is known as an Occlumens.

The most basic form of Occlumency involves clearing one's mind — making it "blank and empty" — in order to prevent a Legilimens from perceiving one's emotions and thoughts. More advanced Occlumency involves suppressing the thoughts, emotions, and memories that would contradict whatever it is an Occlumens wishes a Legilimens to believe; hence, it is not obvious that Occlumency is being used even if the person is lying. It requires a great deal of will power, as with resisting the Imperius Curse, as well as a high degree of mental and emotional discipline. It is also one method of resisting the influence of Veritaserum.